PINK1 alleviates thermal hypersensitivity in a paclitaxel-induced Drosophila model of peripheral neuropathy.

Paclitaxel is a representative anticancer drug that induces chemotherapy-induced peripheral neuropathy (CIPN), a common side effect that limits many anticancer chemotherapies. Although PINK1, a key mediator of mitochondrial quality control, has been shown to protect neuronal cells from various toxic treatments, the role of PINK1 in CIPN has not been investigated. Here, we examined the effect of PINK1 expression on CIPN using a recently established paclitaxel-induced peripheral neuropathy model in Drosophila larvae. We found that the class IV dendritic arborization (C4da) sensory neuron-specific expression of PINK1 significantly ameliorated the paclitaxel-induced thermal hyperalgesia phenotype. In contrast, knockdown of PINK1 resulted in an increase in thermal hypersensitivity, suggesting a critical role for PINK1 in sensory neuron-mediated thermal nociceptive sensitivity. Interestingly, analysis of the C4da neuron morphology suggests that PINK1 expression alleviates paclitaxel-induced thermal hypersensitivity by means other than preventing alterations in sensory dendrites in C4da neurons. We found that paclitaxel induces mitochondrial dysfunction in C4da neurons and that PINK1 expression suppressed the paclitaxel-induced increase in mitophagy in C4da neurons. These results suggest that PINK1 mitigates paclitaxel-induced sensory dendrite alterations and restores mitochondrial homeostasis in C4da neurons and that improvement in mitochondrial quality control could be a promising strategy for the treatment of CIPN.

VAMP7 regulates constitutive membrane incorporation of the cold-activated channel TRPM8.

The cation channel TRPM8 plays a central role in the somatosensory system, as a key sensor of innocuously cold temperatures and cooling agents. Although increased functional expression of TRPM8 has been implicated in various forms of pathological cold hypersensitivity, little is known about the cellular and molecular mechanisms that determine TRPM8 abundance at the plasma membrane. Here we demonstrate constitutive transport of TRPM8 towards the plasma membrane in atypical, non-acidic transport vesicles that contain lysosomal-associated membrane protein 1 (LAMP1), and provide evidence that vesicle-associated membrane protein 7 (VAMP7) mediates fusion of these vesicles with the plasma membrane. In line herewith, VAMP7-deficient mice exhibit reduced functional expression of TRPM8 in sensory neurons and concomitant deficits in cold avoidance and icilin-induced cold hypersensitivity. Our results uncover a cellular pathway that controls functional plasma membrane incorporation of a temperature-sensitive TRP channel, and thus regulates thermosensitivity in vivo.

[Doramectin intoxication in 3 kittens]. / Doramectin-Intoxikation bei drei Katzenwelpen.

This case report describes 3 kittens with suspected doramectin toxicity. In a litter of 7 kittens treated with doramectin, 3 developed neurological symptoms. One kitten showed mild apathy and tremors, while a second one additionally presented behavioral changes and seizures that had to be treated with diazepam. Both kittens recovered completely. A third kitten was presented to us in coma 3 days following treatment with doramectin. Subsequently, this kitten developed behavioral changes such as aggression, hyperesthesia, tremors, and seizures and died 36 hours after presentation. Histopathologic examination of the brain showed cytotoxic edema and polioencephalomalacia. The doramectin dosage of the deceased kitten was 380 µg/kg.

Systematic identification of proteins that elicit drug side effects.

Side effect similarities of drugs have recently been employed to predict new drug targets, and networks of side effects and targets have been used to better understand the mechanism of action of drugs. Here, we report a large-scale analysis to systematically predict and characterize proteins that cause drug side effects. We integrated phenotypic data obtained during clinical trials with known drug-target relations to identify overrepresented protein-side effect combinations. Using independent data, we confirm that most of these overrepresentations point to proteins which, when perturbed, cause side effects. Of 1428 side effects studied, 732 were predicted to be predominantly caused by individual proteins, at least 137 of them backed by existing pharmacological or phenotypic data. We prove this concept in vivo by confirming our prediction that activation of the serotonin 7 receptor (HTR7) is responsible for hyperesthesia in mice, which, in turn, can be prevented by a drug that selectively inhibits HTR7. Taken together, we show that a large fraction of complex drug side effects are mediated by individual proteins and create a reference for such relations.

Resident glial cell activation in response to perispinal inflammation leads to acute changes in nociceptive sensitivity: implications for the generation of neuropathic pain.

Injury or disease affecting the spinal cord is often accompanied by abnormal, chronic pain. Recent estimates suggest that approximately 60% of patients with multiple sclerosis are affected by significant changes in pain sensitivity or experience ongoing neuropathic pain of unknown etiology. Chronic pain is also a significant concern after direct spinal cord trauma. Inflammatory events and the changes in astrocyte and microglia reactivity at the spinal level in response to injury or disease are now recognized as important processes that can initiate pain hypersensitivity. Changes in the structural integrity or permeability of the blood-brain barrier/blood-spinal cord barrier (BBB/BSCB) can facilitate the inflammatory events that result in these abnormal pain states. It remains unclear, however, whether chronic pain in these disorders is dependent on the influx of peripheral leukocytes or whether changes in the reactivity of resident glial cells within the central nervous system alone are sufficient. To address this question, we generated a model of perispinal inflammation that resulted in significant changes in the reactivity of resident astrocytes and microglia within the spinal cord but maintained the integrity of the BSCB. A number of similar changes at the behavioural and cellular level occur in this model that mimic the responses seen in animal models of multiple sclerosis or spinal cord injury (SCI). However, these changes are short lived and resolve over the course of a 2-week observation period. Our findings suggest that the chronicity of pain after injury or disease in the nervous system is dependent on the integrity of the BBB/BSCB.

Enhanced tactile resolution of the contralateral side after surgery and regional anesthesia of the hand.

The purpose of this study was to investigate whether enhancement of tactile resolution (measured with Grating Orientation Task) can be demonstrated for patients undergoing regional anesthesia during hand surgery compared with surgery in general anesthesia and nonoperative controls. Regional anesthesia (nine patients) induced a significant improvement in contralateral tactile resolution at 10 and 24 h after the operation (P<0.01 and <0.05) compared with baseline. In the general anesthesia group (10 patients), tactile resolution improved significantly over time, but to a lesser extent than in the regional anesthesia group. When comparing with the control group (10 individuals), only the regional anesthesia group showed significantly increased tactile resolution at both the time points (P<0.01 and P<0.05), postoperatively.

Transient neurological symptoms after spinal anaesthesia with levobupivacaine 5 mg/ml or lidocaine 20 mg/ml.

BACKGROUND: Transient neurological symptoms (TNS) after spinal anaesthesia have been reported most commonly in association with lidocaine, but have been observed with other local anaesthetics. The aim of this prospective, randomized, double-blind study was to investigate the incidence of TNS after spinal anaesthesia with either levobupivacaine or lidocaine. METHODS: Patients undergoing inguinal hernia, appendectomy, varicose vein or minor orthopaedic operations were included in the study (60 patients; 47 male, 13 female, overall mean age 30 years). All patients had an American Society of Anesthesiologists score of I or II. The patients were randomly assigned to receive spinal anaesthesia with either 20 mg isobaric levobupivacaine (5 mg/ml) or 80 mg isobaric lidocaine (20 mg/ml). Onset of sensory and motor block and side effects were recorded. On post-operative days 1, 2, and 3, patients were interviewed by an investigator blinded to the spinal anaesthetic used. The patients were classified as having TNS if, following recovery from anaesthesia, there was pain in the buttocks, thighs and/or lower limbs. RESULTS: In the levobupivacaine group, one patient (3.33%) experienced TNS, whereas in the lidocaine group, eight (26.6%) experienced TNS (P=0.002). Maximum times to arrival of sensory blocks were shorter with lidocaine (P<0.001). The levobupivacaine and lidocaine groups did not differ significantly in terms of the highest dermatome included in sensory block or motor block grade. CONCLUSION: After spinal anaesthesia with levobupivacaine, the incidence of TNS was much less than after lidocaine. However, it appears that TNS may occur in association with levobupivacaine.

Serotonin 5-HT2A receptor involvement and Fos expression at the spinal level in vincristine-induced neuropathy in the rat.

We recently showed that peripheral and spinal 5-HT2A receptors (5-HT2AR) are involved in a rodent model of neuropathy induced by a nucleoside analogue reverse transcriptase inhibitor. In this paper, we show that 5-HT2AR are also involved in neuropathy induced by an anti-neoplasic drug, vincristine. Vincristine-treated rats (0.1mg/kg, daily i.p. administration for two 5-day cycles) developed thermal allodynia and mechanical hypersensitivity, which decreased in a dose-related manner after epidural injection a 5-HT2A receptor antagonist. Moreover, 5-HT2A-/- mice did not develop vincristine-induced neuropathy contrarily to their 5-HT2A+/+ littermates. In vincristine-treated rats, the number of nociceptive dorsal root ganglion cells expressing the 5-HT2AR was increased by 38%, and 5-HT2AR immunolabelling was enhanced in layers I-IV of the dorsal horn. At the EM level, a 76.3% increase in the density of 5-HT2AR immunopositive axon terminals within superficial layers of the dorsal horn was noted after vincristine treatment. Immunocytochemical study of Fos expression in vincristine-treated rats revealed a significant increase in the number of Fos-positive neurons not only in regions where nociceptive fibres terminate superficial (I-II) and deep layers (V-VI) of the spinal cord, but also in intermediate layers, suggesting that Abeta fibres could be involved in the spinal sensitization observed in this model. Double labelling experiments showed that Fos-positive neurons were endowed with 5-HT2AR immunolabelling in the dorsal horn of vincristine-treated rats. These data provide support to the idea that, in vincristine-induced neuropathy, 5-HT2AR are involved in the sensitization of peripheral nociceptors and spinal nociceptive processing.

Caffeine-related genital skin pain.

Genital hyperesthesia is more recognized in women but may affect men. We report both a female and a male patient in whom caffeine intake was associated with genital hyperesthesia.

Complement activation contributes to leukocyte recruitment and neuropathic pain following peripheral nerve injury in rats.

Complement activation triggers inflammation and has been implicated in neurological diseases associated with pain. However, the role of complement in neuropathic pain has not been clearly defined. In this study, we tested whether complement is activated by partial ligation of the rat sciatic nerve, a widely used model of neuropathic pain, and whether complement activation or inhibition in peripheral nerve influences leukocyte recruitment and neuropathic pain. We found that C3 deposition significantly increased from 6 h to 7 days in the injured nerve and was associated with the extent of thermal hyperalgesia and mechanical allodynia. However, no deposition of the membrane attack complex was detected. Complement activation by endoneurial injection of aggregated rat immunoglobulin G into normal sciatic nerve produced significant thermal hyperalgesia and mechanical allodynia of the ipsilateral hindpaw at 2-7 days after injection. This was accompanied by increased deposition of C3 and recruitment of macrophages at 7 days following injection. Complement inhibition using systemic injections of soluble complement receptor 1 (AVANT Immunotherapeutics, Inc., Needham, USA) into rats markedly suppressed C3 deposition and T-cell and macrophage recruitment to the injured nerve, and produced significant alleviation of thermal hyperalgesia and mechanical allodynia. These results demonstrate that C3 activation in the nerve contributes to increased infiltration of inflammatory cells and to neuropathic pain behaviors following peripheral nerve injury. Complement inhibition may be a potential therapeutic treatment for neuropathic pain.

Activation of cannabinoid CB1 and CB2 receptors suppresses neuropathic nociception evoked by the chemotherapeutic agent vincristine in rats.

BACKGROUND AND PURPOSE: The ability of cannabinoids to suppress mechanical hypersensitivity (mechanical allodynia) induced by treatment with the chemotherapeutic agent vincristine was evaluated in rats. Sites of action were subsequently identified. EXPERIMENTAL APPROACH: Mechanical hypersensitivity developed over the course of ten daily injections of vincristine relative to groups receiving saline at the same times. Effects of the CB1/CB2 receptor agonist WIN55,212-2, the receptor-inactive enantiomer WIN55,212-3, the CB2-selective agonist (R,S)-AM1241, the opiate agonist morphine and vehicle on chemotherapy-induced neuropathy were evaluated. WIN55,212-2 was administered intrathecally (i.t.) or locally in the hindpaw to identify sites of action. Pharmacological specificity was established using competitive antagonists for CB1 (SR141716) or CB2 receptors (SR144528). KEY RESULTS: Systemic administration of WIN55,212-2, but not WIN55,212-3, suppressed vincristine-evoked mechanical allodynia. A leftward shift in the dose-response curve was observed following WIN55,212-2 relative to morphine treatment. The CB1 (SR141716) and CB2 (SR144528) antagonists blocked the anti-allodynic effects of WIN55,212-2. (R,S)-AM1241 suppressed vincristine-induced mechanical hypersensitivity through a CB2 mechanism. Both cannabinoid agonists suppressed vincristine-induced mechanical hypersensitivity without inducing catalepsy. Spinal sites of action are implicated in cannabinoid modulation of chemotherapy-induced neuropathy. WIN55,212-2, but not WIN55,212-3, administered i.t. suppressed vincristine-evoked mechanical hypersensitivity at doses that were inactive following local hindpaw administration. Spinal coadministration of both the CB1 and CB2 antagonists blocked the anti-allodynic effects of WIN55,212-2. CONCLUSIONS AND IMPLICATIONS: Cannabinoids suppress the maintenance of vincristine-induced mechanical allodynia through activation of CB1 and CB2 receptors. These anti-allodynic effects are mediated, at least in part, at the level of the spinal cord.

Anti-allodynic effects of peripheral delta opioid receptors in neuropathic pain.

The analgesic effects of local administration of opioid agonists into peripheral tissues in alleviating pain have been well documented in both clinical and preclinical studies, although few studies have examined their effects in neuropathic pain. In this study, we investigated the anti-allodynic effects of peripherally acting delta opioid receptor (DOR) agonists in a rat model of neuropathic pain. Peripheral nerve injury (PNI) produced a time-dependent decrease in mechanical withdrawal thresholds that was attenuated by local administration into the hind paw of either morphine or the DOR agonist deltorphin II. Using Western blotting techniques, no change in DOR protein expression was detected in DRG ipsilateral to the site of injury compared to contralateral. However, an up-regulation of DOR protein was found in neuropathic DRG compared to sham, suggesting that there may be a bilateral increase in the expression of DOR following PNI. Results obtained from immunohistochemical studies confirmed up-regulation in small and large DRG neurons in neuropathic compared to sham animals. Additionally, there was an increase in DOR protein within the ipsilateral sciatic nerve of neuropathic animals compared to sham and contralateral neuropathic conditions indicating the occurrence of receptor trafficking to the site of injury. Taken together, our findings suggest that functional peripheral DORs are present in sensory neurons following PNI and validate the development of selective DOR agonists for alleviating neuropathic pain.

Intracellular messengers involved in spontaneous pain, heat hyperalgesia, and mechanical allodynia induced by intrathecal dihydroxyphenylglycine.

We investigated the role of two intracellular second messengers, extracellular signal-regulated protein kinase (ERK) and protein kinase C (PKC), in a model of persistent pain using intrathecal (i.t.) (R,S)-3,5-dihydroxyphenylglycine (DHPG). Spontaneous nociceptive behaviours (SNBs), mechanical allodynia (von Frey thresholds) and heat hyperalgesia (plantar test latencies) induced by DHPG were measured in animals pretreated i.t. with membrane permeable inhibitors of ERK (PD 98059) and PKC (GF 109203X). Spinal administration of PD 98059 dose-dependently reduced SNBs, and attenuated both mechanical allodynia and heat hyperalgesia induced by DHPG. GF 109203X treatment also reduced SNBs and heat hyperalgesia, but did not affect mechanical allodynia induced by DHPG. Neither PD 98059, nor GF 109203X, altered mechanical or thermal thresholds in saline-injected control rats. These results suggest that both ERK and PKC are involved in persistent pain associated with the i.t. administration of DHPG.

Participation of peripheral group I and II metabotropic glutamate receptors in the development or maintenance of IL-1beta-induced mechanical allodynia in the orofacial area of conscious rats.

The present study investigated the role of peripheral groups I and II metabotropic glutamate receptors (mGluRs) in interleukin (IL)-1beta-induced mechanical allodynia in the orofacial area of rats. Subcutaneous injection of 10 pg of IL-1beta decreased air-puff thresholds ipsilateral or contralateral to the injection site. The decrease in air-puff thresholds appeared 10 min after the injection of IL-1beta and IL-1beta-induced mechanical allodynia persisted for over 3 h. Pre-treatment with 7-(hydroxyimino) cyclopropa[b] chromen-1a-carboxylate ethyl ester (CPCCOEt) or 2-methyl-6-(phenylethynyl)-pyridine hydrochloride (MPEP), a mGluR1 or mGluR5 antagonist, blocked IL-1beta-induced mechanical allodynia and mirror-image mechanical allodynia produced by a subcutaneous injection of 10 pg of IL-1beta. However, post-treatment with CPCCOEt or MPEP did not affect changes in behavioral responses, which were produced by the IL-1beta injection. Pre-treatment, as well as post-treatment with (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate (APDC), a group II mGluR agonist, blocked either IL-1beta-induced mechanical allodynia or mirror-image mechanical allodynia. The anti-allodynic effects of APDC were abolished by pre-treatment with (2S)-2-amino-2[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid (LY341495), a group II mGluR antagonist. These results indicate that peripheral group II mGluRs are involved in the development and maintenance of IL-1beta-induced mechanical allodynia, while peripheral group I mGluRs are involved in the development of IL-1beta-induced mechanical allodynia. Based on our observations, the peripheral application of group II mGluR agonists may be of therapeutic value in treating inflammatory pain.

Attenuation of capsaicin-evoked mechanical allodynia by peripheral neuropeptide Y Y1 receptors.

Neuropeptide Y (NPY) and its cognate receptors are important modulators of nociception and their expression is significantly altered following injury. In particular, previous studies have demonstrated that the Y1 subtype of NPY receptors inhibits nociceptive transmission from capsaicin-sensitive terminals in the dorsal horn of the spinal cord. The present study evaluated the function of the Y1 receptor on peripheral terminals of primary afferent neurons by testing whether peripherally administered Y1 agonists and antagonists alter capsaicin-evoked mechanical allodynia in rats and capsaicin-evoked immunoreactive calcitonin gene-related peptide (iCGRP) release from isolated superfused rat skin. Treatment with the Y1 agonist [Leu31,Pro34]-NPY (0.5, 1, or 10 nmol) significantly inhibited capsaicin-evoked mechanical allodynia in a dose-dependent manner. This effect was reversible by pretreatment with the Y1 antagonist BIBO3304 (10 nmol). The anti-allodynia produced by the Y1 agonist occurred at a peripheral site of action, because injection into the paw contralateral to the site of the capsaicin injection had no effect on paw withdrawal latencies. In isolated skin, application of [Leu31,Pro34]-NPY (300 nM) significantly inhibited capsaicin-evoked CGRP release. BIBO3304 reversed this inhibition, having itself no effect on capsaicin-evoked iCGRP release. These studies indicate that the activation of peripheral Y1 receptors produces anti-allodynia, possibly via the direct inhibition of capsaicin-sensitive fibers.

Assessment of nociception in acrylamide-induced neuropathy in rats.

Acrylamide was intraperitoneally administered to male Sprague-Dawley rats at four different doses (5, 10, 20 and 30 mg/kg) three times a week for 5 consecutive weeks. Because of motor dysfunction, the 30 mg/kg dose was not used for behavioral pain tests. Clinical status remained good throughout the experiment and no motor deficit was observed at the other doses. We showed that acrylamide administration at low doses and cumulative dose (CD) range of 35-140 mg/kg produced mechanical allodynia and rapid, marked heat (42 degrees C) and cold (10 degrees C) allodynia after tail immersion test. Mechanical and thermal hyperalgesia appeared after higher cumulative doses (70-280 mg/kg), except for cold (4 degrees C) hyperalgesia (20-80 mg/kg). All the modifications persisted throughout all study, except the mechanical hyperalgia. All the cumulative doses tested were lower than those generally reported to induce motor dysfunction (CD>250 mg/kg), confirming that CD may be considered to be a suitable index in assessing neurological signs and suggesting that early detection of acrylamide neurotoxicity would be possible using the sensory tests, especially those for detecting allodynia thresholds.

Excitatory amino acid concentrations increase in the spinal cord dorsal horn after repeated intramuscular injection of acidic saline.

Chronic muscle pain is common and often difficult to treat. In this study, we further characterize a model of chronic muscle pain induced by repeated intramuscular injection of acidic saline. Two injections of acid into muscle separated by 5 days result in secondary mechanical hyperalgesia that lasts for up to 4 weeks. Blockade of spinal NMDA receptors prior to the second injection intramuscular acid injection delays the onset of hyperalgesia, where as the maintenance phase of hyperalgesia, evaluated 1 week after the second intramuscular injection, is dependent on activation of spinal AMPA/kainate and NMDA receptors. In order to determine if behavioral hyperalgesia and glutamate receptor involvement are associated with increased concentrations of excitatory amino acids (EAA), we utilized microdialysis to evaluate extracellular glutamate and aspartate concentrations in the spinal dorsal horn during the first and second intramuscular acid injections, and 1 week after the development of mechanical hyperalgesia. The second intramuscular injection evoked a calcium-dependent increase in both spinal glutamate and aspartate concentrations. Glutamate concentrations within the dorsal horn were also increased 1 week after the second acid injection. Our data suggest increased release of spinal EAAs in the dorsal horn contributes to the development and maintenance of hyperalgesia.